Fastener for the osteosynthesis of the spinal column

Abstract

A fastener for relieving stress on a disc adjacent at least two vertebrae which are mechanically connected during osteosynthesis of the spinal column which fastener includes a fastening rod having a first portion which is secured to the at least two vertebrae by tightening elements provided on pedicle screws and a second portion, whose diameter is smaller than that of the first portion, which slides in a guidance element which is anchored in of the vertebra located adjacent the at least two vertebrae which are mechanically locked relative one another.

We claim: 
     
       1. A fastener for implanting to spaced vertebrate for relieving stress on a vertebral disc of a vertebral stage of patient's spinal column which is adjacent at least two vertebral stages which are mechanically united to one another and wherein each of the vertebral stages includes a vertebra having pedicles, the fastener comprising, a fastener rod having first and second portions, said second portion having a diameter which is less than the diameter of said first portion, at least two pedicle screw means, each pedicle screw means having a portion which is adapted to be anchorable into adjacent pedicles of the vertebrae of the at least two vertebral stages, each of said pedicle screw means including tightening means for securing said first portion of said rod to said at least two pedicle screw means so as to be in fixed relationship to the at least two vertebral stages when said fastener is in use, a guidance means having a screw portion which is adapted to be anchored into a pedicle of the vertebra of the next adjacent vertebral stage and a head portion, said head portion having an open passageway, said second portion of said fastener rod being continuously slidably engaged within said open passageway when said fastener is implanted in the vertebrae and said first portion of said rod is secured to said at least two pedicle screw means which are fixed to the at least two vertebral stages and said guidance means is secured to the next adjacent vertebral stage, whereby said fastener relieves stress on the disc adjacent the at least two vertebral stages when in use. 
     
     
       2. The fastener of claim 1 in which said head portion of said guidance means includes a bore having two lateral notches on opposite sides thereof, a disk mounted within said bore, said open passageway extending through said disk and means extending through said head portion for retaining said disk within said bore. 
     
     
       3. The fastener of claim 2 in which said bore has a spherical internal profile, and said means for retaining said disk within said bore includes an adjusting screw extending through said head portion. 
     
     
       4. The fastener of claim 3 in which said disk has an external profile complimentary to that of said bore so as to form a ball-joint like coupling. 
     
     
       5. The fastener of claim 4 in which said passageway includes an inner and rounded surface for reducing the area of contact and frictional resistance between said disk and said second portion of said fastener rod. 
     
     
       6. The fastener of claim 5 in which said disk includes a hole spaced from said passageway which is smaller in diameter than said passageway. 
     
     
       7. The fastener of claim 6 in which said screw portion includes a self-tapping thread. 
     
     
       8. The fastener of claim 1 in which said head portion includes a spherical head element which is generally coaxial to said screw portion, a pair of symmetrical washers each having a conically shaped open bore therethrough, said spherical head element being pivotably seated within said open bore of one of said washers, each of said washers including a notch which extends generally perpendicularly with respect to said open bore, said notches being in opposing relationship with respect to one another, ring means mounted between said notches, said ring having a ball-joint mounted therein, said open passageway extending through said ball-joint. 
     
     
       9. The fastener of claim 8 in which each of said notches includes a groove, said ring means including portions receivable within said grooves. 
     
     
       10. The fastener of claim 9 in which said grooves are v-shaped in profile. 
     
     
       11. The fastener of claim 8 in which said guidance means includes a threaded rod portion extending above said spherical head element, and a nut engageable with said threaded rod portion. 
     
     
       12. The fastener device of claim 11 in which each of said washers includes a flat inner bearing surface and an opposite semi-spherical outer surface, said nut having a lower semi-spherical surface which is engageable with the semi-spherical outer surface of one of said washers when said nut is threaded on said threaded rod portion of said guidance means. 
     
     
       13. The fastener device of claim 12 in which said spherical head element of said guidance means includes a conical portion having a roughened outer surface. 
     
     
       14. A fastener assembly for implanting to spaced vertebrae for relieving stress on a vertebral disc of a vertebral stage of patient's spinal column which is adjacent at least two vertebral stages which are mechanically united to one another and wherein each of the vertebral stages includes a vertebra having pedicles, the fastener assembly comprising, two essentially parallel fastener units, each of the units including a fastener rod and at least two pedicle screw means, each pedicle screw means having a portion which is adapted to be anchorable into adjacent pedicles of the vertebrae of the at least two vertebral stages, and each of the pedicle screw means including tightening means for securing said fastener rod to said at least two pedicle screw means so as to be in fixed relationship to the at least two vertebral stages, a pair of guidance means each having a screw portion which is anchorable into a pedicle of the vertebra of the next adjacent vertebral stage and a head portion, each head portion having an open passageway, each of said fastener rods being continuously slidably engaged with a separate one of said open passageways of said air of guidance means when said fastener assembly is implanted in the vertebrae and said first portion of said rods is secured to said at least two pedicle screw means of each of said fastener units which are fixed to the at least two vertebral stages and said pair of guidance means are secured to the next adjacent stage, whereby said fastener assembly relieves stress on the disc adjacent the at least two vertebral stages. 
     
     
       15. The fastener of claim 14 in which each of said fastener rods includes first and second portions, said second portion having a diameter which is less than the diameter of said first portion, said second portion of said fastener rods extending through said open passageway of said head portion of said guidance means.